X-Ray and Electrical Conductivity Study of the Fluorite Phase in the System ZrO2–CaO

Abstract

In the ZrO2–CaO system cubic solid solutions of the fluorite-type structure are formed between 12 and 22 mole % CaO for specimens fired at 2000°C and subsequently quenched from 1400°C. The lattice parameter increased linearly from 5.125 to 5.144 Å with increasing CaO content. Results of x-ray diffraction intensity studies favored the oxygen-ion vacancy model over the cation interstitial model for these solid solutions. As the CaO content was increased from 13 to 20 mole %, the electrical conductivity at 1000°C decreased from 5×10—2 to 6×10—3 Ω—1 cm—1 and the activation energy increased from 1.11 to 1.35 eV. Specimens heated at 1000°C for one week showed extra x-ray diffraction lines. These data coupled with accompanying changes in electrical conductivity are discussed in terms of an order—disorder transition.

Oxygen Self-Diffusion in Cubic ZrO2 Solid Solutions

“…The temperature of l400°C is the temperature where Tien and Subbarao (1963) However, the agreement of three measurements by the different investigators suggests that the oxygen diffusion in the low-temperature range is controlled by the same single mechanism, being independent of the phase transition on the phase diagram. The results are interpreted that the high-temperature regime with the lower activation energy is for the disordered structure and the low-temperature regime with the higher activation energy for some ordered structure in a meta-stable state.…”

Origin of the hump on the left shoulder of the X-ray diffraction peaks observed in Y2O3-fully and partially stabilized ZrO2

“…Accordingly, various microstructural studies of stabilized zirconia have been conducted [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Many microstructural studies on its hardening mechanism have been conducted by examining phase transformations and performing phase determination by X-ray diffractometry (XRD) [7][8][9][19][20][21][22].…”

“…Accordingly, various microstructural studies of stabilized zirconia have been conducted [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Many microstructural studies on its hardening mechanism have been conducted by examining phase transformations and performing phase determination by X-ray diffractometry (XRD) [7][8][9][19][20][21][22]. Therefore, there are many reports about the crystal structures of zirconia, and crystal-structural changes and phase transformation in various conditions of dopant, composition, temperature, and heat treatment have been reported [23][24][25][26][27][28][29][30][31][32].…”

Feasibility Study on Advanced Solid-State Oxygen Sensors.

“…The solid solutions of calcia (CaO), yttria (Y 2 0 3 ), or other rare-earth oxides in zirconia (Zr02) are known to change its crystal structure (18)(19)(20)(21)(22)(23). Within certain concentration ranges, such solutions crystallize ig a cubic phase which is stable in the desired temperature range of 300-900 C, and show approximately pure oxygen ion conductivity.…”